Commercial airliners and other conventional aircraft typically include environmental control systems that provide conditioned air for the passengers and crew and for other purposes. Conventional environmental control systems (ECSs) use air that is “bled” off the compressor of each jet engine upstream of the combustor. The temperature and pressure of this “bleed air” can vary widely depending on the thrust setting of the engine. For this reason, ECSs typically include one or more heat exchangers, compressors, and/or turbines to adjust the temperature and pressure of the air before it flows into the cabin.
Using engine bleed air for cabin air conditioning can reduce engine fuel efficiency. To avoid this result, some newer aircraft (such as the Boeing 787 aircraft) have “more electric” air conditioning systems that use outside air from ram air inlets for this purpose. Such systems, however, typically require at least two separate ram air inlets for each air conditioning pack. The first ram air inlet provides air to electric-motor-driven cabin air compressors, which supply high pressure air to the air conditioning pack. The second ram air inlet provides cooling air to the air conditioning pack heat exchanger. While having a dedicated high pressure recovery ram air inlet for the cabin air compressors can reduce the power requirements of compressors, the additional inlet adds drag, weight, cost and complexity to the aircraft which can offset gains in fuel efficiency.